This invention relates generally to backplanes, and more specifically to backplane wiring systems for highly interconnected, high-speed modular digital communications systems such as routers and switches.
A backplane generally comprises a printed circuit board having a number of card connection slots or bays. Each slot or bay comprises, e.g., one or more modular signal connectors or card edge connectors, mounted on the backplane. A removable circuit board or xe2x80x9ccardxe2x80x9d can be plugged into the connector(s) of each slot. Each removable circuit board contains drivers and receivers necessary to communicate signals across the backplane with corresponding drivers and receivers on other removable circuit boards.
One or more layers of conductive traces are formed on and/or in the backplane. The traces connect to individual signal connection points at the various slots to form data lines and control lines.
Router backplanes present a challenging area of circuit board design (for convenience, routers and switches will be referred to herein collectively as xe2x80x9croutersxe2x80x9d, as the technical distinctions between the two are unimportant to the invention as described herein). By their very nature, configurable modular routers require a high degree of interconnectivity between their removable router cards. With any appreciable number of cards, it becomes infeasible to build large parallel point-to-point connection buses between each pairing of the cards. This limitation hinders further growth in large router throughput, as the next generation of large routers may well see throughput requirements measured in terabits-per-second. As such throughput requirements may require several tens (or even hundreds) of logical ports to exchange data simultaneously at twenty to one-hundred Gigabit-per-second (Gbps) speeds, it can be appreciated that the connectivity and throughput requirements placed on large router backplanes are extreme.
Many router manufacturers, believing that the limits of electrical circuit boards have been reached in the area of large router backplanes, are now designing optical backplanes for their next-generation products. Optical backplanes avoid some of the most problematic characteristics of electrical backplanes, such as trace density, signal attenuation, signal reflection, radiated noise, crosstalk, and manufacturing limitations-characteristics that become increasingly significant as single-trace signaling speeds push into the multi-Gbps range. Optical backplanes, however, come with their own set of problems, chief among these being cost and complexity.
This disclosure describes an electrical router backplane that overcomes many of the electrical and mechanical limitations of large prior art electrical backplanes, and methods for its design and fabrication. Generally, this backplane comprises multiple high-speed signaling layers of differential signaling pairs, separated by ground layers. Preferably, power distribution layers and/or low-speed signaling layers are embedded near the center of the backplane stack, between outer groups of high-speed signaling layers. Various additional design features can be combined within this general architecture to produce a backplane that has been tested for reliable communication at single trace pair differential-signaling speeds up to 10.7 Gbps, 200-ampere power distribution, and overall backplane throughput greater than 1.6 Terabits/second.
In the present disclosure, a wide range of new backplane features and manufacturing processes are disclosed, each of which contributes to the overall success of the backplane design. Preferably, these aspects are combined in a single backplane to provide an accumulation of the benefits of each aspect.